As semiconductor devices are aggressively scaled down, the number of photoresist masking steps used in the photolithography process has significantly increased due to various etching and/or implanting requirements. Consequently, the number of post-masking cleaning steps has also increased. After a layer of photoresist is patterned on a semiconductor wafer and then subjected to a fabrication process, such as plasma etch or ion implantation, the patterned photoresist layer must be removed without leaving photoresist residue, which may detrimentally affect the resulting semiconductor device with respect to performance and reliability.
Traditionally, semiconductor wafers have been cleaned in batches by sequentially immersing the wafers into baths of different cleaning fluids, i.e., wet benches. However, with the advent of sub-0.18 micron geometries and 300 mm wafer processing, the use of batch cleaning has increased the potential for defective semiconductor devices due to cross-contamination and residual contamination. In order to mitigate the shortcomings of batch cleaning processes, single-wafer spin-type cleaning techniques have been developed. Conventional single-wafer spin-type cleaning systems typically include a single fluid delivery line to dispense one or more cleaning fluids, such as deionized (DI) water, standard clean 1 (SC1) solution and standard clean 2 (SC2) solution, onto a surface of a semiconductor wafer in an enclosed environment. After the semiconductor wafer is cleaned, the wafer is usually rinsed using DI water and then spin-dried using Isopropyl Alcohol (IPA) by rotating the wafer at a high rotational speed.
An important aspect of a single-wafer spin-type cleaning system is the rotating of the semiconductor wafer. Since the semiconductor wafer is typically rotated at high speeds, especially during the spin-drying process, the mechanisms of the single-wafer spin-type cleaning system that hold and rotate the semiconductor wafer must be well designed. Inferior design of these mechanisms may cause instability at high rotational speeds, which may result in damage of the semiconductor wafer being cleaned.
Some conventional single-wafer spin-type cleaning systems include an acoustic transducer to apply megasonic or ultrasonic energy to the front surface of a semiconductor wafer to assist in the cleaning of the wafer. However, direct application of acoustic energy to the front surface of the semiconductor wafer where delicate patterns are formed may damage these patterns. Consequently, the acoustic transducer in some conventional single-wafer spin-type cleaning systems is positioned to apply megasonic or ultrasonic energy to the back surface of the semiconductor wafer. Since the acoustic energy must travel through the semiconductor wafer to reach the front surface of the wafer, the acoustic energy applied to the back surface of the wafer is attenuated to reduce the possibility of damage to the delicate patterns formed on the front surface of the wafer.
A concern with conventional single-wafer spin-type cleaning systems with an acoustic transducer is that the acoustic energy generated by the acoustic transducer is usually applied uniformly to the front or back surface of a semiconductor wafer without any control of the intensity of the acoustic energy being applied to the wafer surface. Consequently, the amount of applied acoustic energy at a particular region of a semiconductor wafer cannot be controlled.
In view of the above-described concerns, there is a need for a single-wafer spin-type cleaning system and method for wet cleaning a semiconductor wafer that provides increased stability at high rotational speed and increased control of acoustic energy that is applied to the semiconductor wafer.